Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-02-23
2002-02-05
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S070000, C347S071000
Reexamination Certificate
active
06343855
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a ferroelectric element and, more particularly, to a ferroelectric element which is advantageously usable as a piezoelectric element in ink jet printers and other devices. The ferroelectric element according to the present invention, as compared with the conventional ferroelectric element, can be a thick film having a thickness of 10 to 20 &mgr;m and, at the same time, can avoid cracking at the time of the film formation. Further, since fine particles of a ferroelectric precursor can be previously formed in the course of preparation of the ferroelectric element by a sol-gel process, a more dense element can be prepared in a shorter time. Furthermore, the ferroelectric element of the present invention can be advantageously produced from a green sheet thereof. In this case, the firing temperature may be lower than that in the prior art process, and the range of selection of an electrode material to be placed on both of the green sheet necessary for the development of ferroelectricity and piezoelectricity can be broadened. The present invention also relates to a process for producing the above ferroelectric element and a piezoelectric ink jet head using the above ferroelectric element as a piezoelectric element. The term “piezoelectric” and the term “ferroelectric” used herein are defined as follows. Materials, which, when an external force (a stress from the outside) is applied to a crystal thereof, develop polarization, are called piezoelectrics, and, among the piezoelectrics, those wherein the polarization can be reversed by an external electric field are expressly called ferroelectrics.
BACKGROUND ART
In recent years, in office automation (OA) equipment, such as word processors, personal computers, facsimile machines, various measuring instruments, such as medical measuring instruments, and other devices, ink jet printers have been extensively used for printing information from these devices at a high density. As well known in the art, in the ink jet printer, an ink droplet is ejected from a head section of the printer and deposited directly onto a recording medium, such as recording paper, to perform monochrome or color printing. The ink jet printer has many advantages including that printing can be performed on even a three-dimensional recording medium, running cost is low since plain paper can be used as the recording medium, the head can be simply loaded, the need to provide the step of transfer, fixation and the like can be eliminated, color printing is easily performed, and a sharp color printed image can be provided. The head section of the ink jet printer can be classified into several types according to the method for ejecting ink droplets from the head section. Among them, a typically and advantageously used one is a piezoelectric ink jet head.
The piezoelectric ink jet head generally comprises: a plurality of ink chambers which are disposed at equidistant spaces and function as an ink flow passage and a pressurizing chamber for ejecting an ink; and a nozzle plate mounted on the front end of the ink chambers and equipped with nozzles, for ejecting an ink, corresponding respectively to the ink chambers; and pressurizing means for pressurizing an ink within the ink chamber in response to a demand for printing. The pressurizing means comprises a piezoelectric element, and an electrostrictive effect attained by this piezoelectric element is utilized to create a pressure wave within the ink chamber, filled with an ink, in the head section, permitting the ink to be ejected through the nozzle in the head section.
Ferroelectric elements have been extensively used as a piezoelectric element in the above ink jet head or as, for example, capacitors, actuators, memories, and other elements. A ferroelectric element consists essentially of a ferroelectric body or a ferroelectric material. Examples of typical ferroelectric materials include lead zirconate titanate (PZT) generally represented by Pb(Zr,Ti)O
3
, (Pb,La)(Zr,Ti)O
3
(PLZT), and Pb(Mg
1/3
Nb
2/3
)O
3
(PMN). In particular, it is known that ferroelectrics containing lead (Pb) as one metal component, including PZT, have large remanence, specific permittivity, and piezoelectric constant and possess excellent piezoelectricity and ferroelectricity. In the present specification, the ferroelectric material will be described particularly with reference to PZT.
The above ferroelectric elements, particularly thin film elements of PZT, have hitherto been produced by various film forming methods, such as sputtering, sol-gel process, CVD, and laser ablation, or methods related thereto. When the thin film element is formed particularly in a large thickness of 10 to 20 &mgr;m, a method has been used wherein the film thickness is increased by prolonging the film formation time or by repeating the film formation procedure. Further, when a PZT element having a perovskite structure is produced, firing is generally performed in a high temperature atmosphere of 500 to 800° C.
Among the film formation methods, the sol-gel process which is particularly included in the range of a solution preparation method is advantageous in that a high-purity thin film of PZT can be formed, a starting material can be quantitatively dissolved in a solution and, hence, the composition of the formed thin film of PZT can reflect the composition of the starting material used, which facilitates the control of the composition and can provide a thin film of PZT having high surface smoothness by repetition of spin coating and firing. The solvent used in the preparation of a sol-gel solution is in many cases an alcohol solvent because the metal for PZT takes the form of a metal alkoxide or a metal salt of an organic carboxylic acid. The solution prepared by the sol-gel process may be coated onto a substrate, for example, by spin coating or dip coating to form a film. In this film formation, addition of a photosensitive resin to the solution enables patterning by photoetching.
More specifically, for example, Japanese Unexamined Patent Publication (Kokai) No. 6-112550 discloses a method for forming a thin film of PZT which comprises hydrolyzing a metal alkoxide as a PZT material to prepare a sol solution, adding a soluble organic polymer, for example, polyethylene glycol monomethyl ether, to the solution and thoroughly stirring the solution. Subsequently, a platinum electrode is formed on a silicon substrate, a sol solution prepared above is spin-coated on the electrode, and the coating is heated to about 350° C. The prefiring results in the formation of a porous thin film of a gel. The same starting material as the above PZT material is hydrolyzed to form a sol solution. In this case, however, no polyethylene glycol monomethyl ether is added. The sol solution is spin-coated onto the above porous thin film of a gel to form a coating which is then dried by heating at 400° C. The resultant thin film is fired in an oxygen atmosphere for 15 hr. The firing temperature is generally 600 to 700° C. Thus, a thin film of PZT having a perovskite structure can be formed through a series of steps. In this film formation method, a sol is filled into pores of the porous thin film of a gel. This reduces the porosity and can offer high Young's modulus and consequently excellent electric properties. Further, since the size of the pore is not more than 1 &mgr;m, no cracks are created.
Japanese Unexamined Patent Publication (Kokai) No. 6-119811 discloses a process for producing a ferroelectric thin film element, comprising producing a ferroelectric thin film by a sol-gel process using a metal alkoxide as a main starting material, wherein particles of a ferroelectric oxide are added to a sol prepared by hydrolyzing the starting material followed by homogeneous mixing to prepare a coating liquid. In this film formation method, addition of ferroelectric oxide particles to the sol enables a thick film to be easily formed and, in addition, results in the formation of a thin film of PZT having excellent properties and electric characteristic
Aizawa Mamoru
Sakamaki Shin-ichi
Takahashi Yukimi
Toki Motoyuki
Yamada Yorinobu
Barlow John
Citizen Watch Co. Ltd.
Do An H.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
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